Magnetostrictive relay



July 21, 1959 H. .1. McCREARY MAGNETOSTRICTIVE RELAY Filed 001:. 1', 1957 INVENTOR.

Harold J. McCreary BY a? Affy.

United States Patent 2,896,044 Patented July 21, 1959 MAGNETOSTRICTIVE RELAY Harold McCreary, Lombard, Ill.,-assignor to General Telephone Laboratories, Incorporated, Northlake, Ill., aeiirporationofDelaware Application October 1, 1957, Serial No. 687,392

2 Claims. (Cl. 200-87) This case relates to relays and more particularly to those of the magnetostrictive type.

In the past many relays have been made utilizing either magnetic attraction or the thermal action of bimetals to perform the circuit control function. More recently magnetostrictive action has been used in circuit control. In this type of application, a spring or actuating member is made by bonding together two metals having dissimilar magnetostrictive coefficients. By introducing a magnetic field to the actuator, the spring becomes magnetized. When the spring has become magnetically saturated, the dissimilar metals expand differently and the spring assumes a bow or arcuate shape. In bowing the spring makes contact with a stationary member thereby closing an external circuit.

Practical applications of the magnetostrictive principle have not generally been used to achieve a relay effect and where they have been used, temperature problems have arisen. Magnetostrictive action is somewhat similar to thermal expansion and changes in thermal conditions cause relays using bimetals to be generally unstable.

Further, the use of magnetostriction produces eltects of far greater magnitude than thermic action. This is due to the fact that certain ferro-magnetic materials exhibit negative coefficients of magnetostriction and others positive. Thus by proper combination of materials, the relative reaction of materials to magnetic saturation can be used to produce a positive, snap-acting relay.

It is an object of the present invention to provide a magnetostrictive relay which is imprevious to temperature change and which remains stable under normal temperature conditions.

It is a further object of the invention to provide a relay having a pair of identical bi-metallic springs. One spring is to be magnetized to effect an electrical contact to the other spring. Further, these springs will react to ambient temperature changes in a like manner to maintain a contact gap between the springs of constant dimension.

A feature of the invention resides in the provision of two bi-metallic contact springs, each having one of the bimetals in like relative position, so that each spring will deflect a like amount due to temperature changes.

The single embodiment of the invention is shown in the drawing. The relative sizes and thicknesses have been exaggerated to point up the novelty of the invention.

Shown is the relay .10 having a mounting base 11 to which is secured spring pileup 15. The spring pileup includes bi-metallic springs 20 and 30 separated by insulators 36 and mounted in place.

Springs 30 has cut in its body a rectangular window 4% and has mounted to one side of the window, toroidal wound coil 35. The purpose of this window or cutout is to provide a complete magnetic path through the spring. Spring 30 is the movable spring and spring 20 is the sta tionary one.

Spring 30 is constructed having two metallic layers bonded together. Layer 31 is of a metal having a negative coeflicient of magnetostriction such as nickel. Layer 2 32 is a ferrous alloy having-a positive coefficient of magnetostriction. An example of-ametal which will serve well as the ferrous alloy is 45 Permalloy. Representative values of magnetostriction for these materials may be found on page 631 of Ferromagnetism by Bozorth, published in 1951 byVan Nostrand. Typical values for these metals include an expansionfor45. Permalloy of 2 5 x 10 per :unit length while ni ckel. shows "a contraction .of

3O l0- per unit length. 'The values listed are magnetizations to saturation.

When a current is passed through coil 35, a magnetic field is set up in spring 30. When the spring is saturated, the layer 31 contracts and the layer 32 expands. Spring 30 then assumes a bow shape and contact 33 is moved firmly against contact 23, thereby closing an electrical circuit.

Spring 20 is also constructed of two layers, one layer 21 of negative magnetostrictive material and the other layer 22 of material having a positive coefficient of magnetostriction. The metals used are the same as those used in spring 30 and are relatively positioned in an identical manner to those in spring 30. Due to the like positioning, thermal effects are minimized. Thus when ambient temperature changes affect spring 20, they affect spring 30 to the same degree. The net result is a constant size gap between contacts 23 and 33. Spring 20 and 30 are always maintained in a parallel relationship due to temperature differences of the ambient surroundings.

By the use of window 40 internally within a spring, a solid metallic circuit can be provided to fully utilize the high permeability of the ferrous materials used. With a solid magnetic circuit, the permeability of the circuit closely approximates the values listed previously for the bimetals. Further since the entire magnetic circuit is composed of the bimetals themselves, a greater length of bimetal is provided to result in a greater actual dimensional change. This, of course, is true since expansion and contraction ratios are based on net change per unit length. Also, the high permeability of the responsive material such as Permalloy is in fact operative throughout the magnetic circuit and can be easily saturated with magnetic flux.

While a single embodiment has been shown, it will be understood that many variations and applications within the scope of the present invention will readily occur to persons skilled in the art. For instance, a make spring combination has been shown. Over the embodiment shown it would require no inventive skill to substitute a break combination. It is the intention therefore to be limited only as indicated by the appended claims.

What is claimed is:

1. A circuit closing device comprising a plurality of bimetallic cantilever contacting springs and means for producing a magnetic flux in one of said springs, each of said springs comprising a pair of dissimilar metals bonded together, said dissimilar metals including a first metal having a positive coetlicient of magnetostriction and a second metal having a negative coeflicient of magnetostriction, each of said springs having the metals aligned in the same relative positions, all said springs responsive to ambient temperature changes to assume relatively parallel positions when acted on only by temperature, one of said springs having a cutout therein, said flux producing means comprising an electromagnetic coil mounted to said cutout, said one spring including a complete magnetic path for magnetic fiux around said cutout, said one spring capable of assuming an arcuate shape to contact another of said springs when said one spring is saturated by a magnetic flux.

2. A circuit closing device comprising a plurality of cantilever springs, each of said springs comprising a pair of dissimilar ferrous metals of high permeability bonded together and a contacting surface, one of said springs having a centrally located fenestration therein, a toroidal Wound coil mounted to a side of said fenestration, another of said springs mounted parallelly to said first spring and having metals therein in the same relative position as said first spring, said springs thereupon assuming parallel positions normally, a solid metallic magnetic path of said high permeability materials within said one spring to distribute flux from said coil throughout said one spring, the metals in said one spring magnetostrictively combined to assume an arcuate shape on saturation by flux from said coil, the

contacting surfaces of said one and other springs meeting on saturation of said one spring.

References Cited in the file of this patent UNITED STATES PATENTS Delanty Feb. 11, 1936 Massa July 5, 1949 Leslie et al Sept. 25, 1956 FOREIGN PATENTS 1 Great Britain June 7, 1950 

